He seems to have been reading the comment that I made in this newsgroup on the 8th of July.

in the "Met Met Office explanation of Heathrow record" I did post "it would be interesting to see a graph of aircraft takeoff and landings for that day and just wonder if they were just clearing a bit of a delay on long distance 747's at around the time the maximum occurred"

Having worked at RAF stations for a good part of my observing career, it does seem plausible depending on the exact siting of the Stevenson screen.

Interestingly 6 (or maybe 7) of the 14 record breaking sites that the Met Office list in their blog are also on airfields!